If 27 (x + y)3 - 8(x - y)3 = (x + 5y) (Ax2 + By2 + Cxy), then what is the value of (A + B - C)?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 16
Concept
a3 - b3 = ( a - b) (a2 + b2 + ab)
Application
27(x + y)3 - 8(x - y)3 = [3(x + y)]3 - [2(x - y)]3
[3(x + y) - 2(x - y)] [(3x + 3y)2 + (2x - 2y)2 + 3(x + y) × 2(x - y)]
(x + 5y) (19x2 + 7y2 + 10xy)
Upn comparing, we get
A = 19, B =7, C = 10
Therefore, A + B - C = 19 + 7 - 10 = 16